The maintenance of an effective epithelial barriir, which can minimize the penetration of toxic by-products from the microbial flora into the connective tissue, represents one of the most important mechanisms in the resistance of the host to infection. We have previously observed that the basement membrane represents the rate-limiting barrier to the penetration of non-Keratinized mucosal epithelium by bacterial endotoxin and, more recently, inulin and dextran. We have also noted that acute ascorbate deficiency can increase mucosal permeability to these three agents. Current studies focus on the effects of acute folate and Vitamin A deficiency on oral mucosal permeability to dextran (MW 70,000), and also on the effects of these deficiencies on basement membrane biosynthesis. In addition, static, autoradiographic studies have suggested that the mucosal barrier may possess "directionality." That is, the speed of penetration may depend upon the direction of penetration. This observation is currently being evaluated in a dynamic permeability assay system. BIBLIOGRAPHIC REFERENCES: "Autoradiograahic Study of the Penetration of Radiolabelled Dextrans and Inulin through Non-keratinized Oral Mucosa in Vitro". M.C. Alfano, A.I. Chasens and C.W. Masi. J. Periodont. Res. 12, 1977, in press.